1. Field of the Invention
The present invention relates to a power steering lock unit for locking the steering in an automobile or the like.
2. Description of the Related Art
Conventionally, with the object of preventing theft, power steering lock units used for locking the steering in an automobile or the like have an engaging concave portion provided on the outer periphery of a steering shaft which rotates in accordance with a steering operation. When a driver performs an engine stopping operation using a key or the like, a retractable lock bolt advances and engages the engaging concave portion due to the action of an actuator, and thus the rotation of the steering shaft is restricted and the steering is locked. On the other hand, when the driver performs an engine starting operation using a key, the lock bolt retracts from the engaging concave portion and the engagement is released, thus the restriction of the rotation of the steering shaft is released and the steering is unlocked. After the steering is unlocked the engine can be started.
With this type of power steering lock unit, it is necessary to prevent with certainty the lock operation from being performed while the automobile is running, even if a microcomputer serving as control means malfunctions due to abnormal rises in temperature. Moreover, even in the case that the steering does become locked, it is necessary that the steering can be quickly unlocked. Thus it is necessary to detect (obtain) with certainty the position of the lock bolt using a sensor. The sensor also plays a role on detecting the stop timing of the actuator and preventing excessive operation of the actuator.
The following is information from a prior art document that is related to such a power steering lock unit.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2006-36110.
Japanese Unexamined Patent Application Publication No. 2006-36110 discloses a structure for detecting the position of a lock bolt, in which a magnet is disposed on the lock bolt or a lock stopper which is interlocked with the lock bolt, and in which the position of the lock bolt is detected by detecting the magnetism of the magnet with a Hall IC.
However, with the power steering lock unit in Japanese Unexamined Patent Application Publication No. 2006-36110, there are cases in which rattling movements from vibrations during running of the automobile, inaccuracies in assembling each part, or the like can cause the magnet and the Hall IC to separate from a detection range so that the detection state of the Hall IC is unintentionally switched, and thus the position of the lock bolt cannot be detected with certainty. In this case, even if for example the steering is unlocked during running of the automobile, an incorrect operation occurs, such as the operation of a failure determination function of the power steering lock unit, or the operation of an alarm function, when the unlocked state cannot be detected.